Elemental microanalysis

Another traditional method used for polymer support characterization is elemental analysis. Its use as an accurate quantitative technique for monitoring solid-phase reactions has also been demonstrated [146]. Microanalysis can be extremely valuable if a solid-phase reaction results in the loss or introduction of a heteroatom (usually N, S, P or halogen). In addition, this method can be used for determination of the loading level of a functional group (e. g. usually calculated directly from the observed microanalytical data). For example, in many cases, the displacement of chloride from Merrifield resin has been used as a guide to determine the yield of the solid-phase reaction. 

Other destructive methods that are widely used for qualitative analysis, on account of their simplicity and speed, are color tests specific for particular functional groups. These have been developed mainly for the detection of amines in SPPS. Titrations and derivatizations can also be performed, but are often inaccurate, time-consuming and of limited use. A review of all these methods has been published recently by Kay et al. [148] More recently, new color tests for alcohol [149, 150], thiol [151] and aldehyde [152, 153] functionalities have also been reported. 

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In a combined elemental microanalysis (to determine the C, H, N and Cl contents of char), TGA, DSC, mid-infrared and NMR study of the char forming process in polychloroprene, CPMAS solid-state 13C NMR was used to probe for structural changes that occurred during the degradation steps [88]. The NMR study supplied both valuable extra detail and confirmatory and complementary information. It was observed that while the dehydrochlorination of polychlo-prene proceeded, there was loss of sp3-hybridised carbon and commensurate... 

For both the Si02-g-PS and the Si02-g-PDMS systems the surface coverage of the polymer was determined by elemental microanalysis. In the former case this was supplemented by thermo-gravimetric analysis. 

The T values quoted in table III were obtained from elemental microanalysis determinations. In order to check the reliability of these values, thermogravimetric (TGA) studies were carried out on several of the Si02 g-PS samples. The weight (w) of the sample is followed as a function of temperature and hence a, the fractional weight loss, determined, where a is given by... 

The simplest formula for an organic compound is called its empirical formula. This shows the elements present in the compound and the simplest ratio of the atoms of these elements in the compound. For example, ethane (C H ) has an empirical formula of CHj, whereas benzene (C H ) has an empirical formula of CH. Empirical formulae can be determined by a technique known as elemental microanalysis and you will find out more about this on p. 72. 

A number of experimental techniques are carried out in organic chemistry to confirm that the correct compound has been synthesised during a reaction, or to identify unknown compounds. Some of these techniques are laboratory-based and are discussed in the Researching Chemistry section. Organic chemists rely heavily on a number of other techniques to identify compounds. These include elemental microanalysis, mass spectrometry, infrared spectrometry and NMR spectrometry. 

Elemental microanalysis is used to determine the masses of the elements present in a sample of an organic compound to work out its empirical formula. 

Elemental microanalysis (or combustion analysis) can be used to determine the empirical formula of an organic compound. 

Mass spectrometry is often used alongside elemental microanalysis. 

Sometimes elemental microanalysis results are given as percentages by mass. The process used to calculate the empirical formula from the percentage by mass is similar to that just shown, assuming the total mass of the sample to be 100 g. 

Elemental composition Mg 60.32%, O 39.68%. The oxide can be identified nondestructively by x-ray methods. Oxygen content may be determined by elemental microanalysis. Magnesium may be analyzed by AA or ICP following dissolution of the oxide in nitric acid and appropriate dilution with water. 

Elemental composition S 25.23%, H 0.79%, N 11.02, 0 62.95%. Nitrosylsulfuric acid may be analysed by IR, NMR and mass spectrometry, as well as by elemental microanalysis. Wet analysis involves hydrolyzing the compound in the presence of excess NaOH and measuring excess base by potentiometric titration. 

Analytical issues (i) X-ray elemental microanalysis (ii) Ion-selective electrodes for chnical use. (iii) Electron probe and electron energy loss analysis. (iv) Intracellular measurements . (v) Determination of Mg in human tissues and fluids . (vi) Trace elements in hair. (vii) Determination of Ca and Mg in wines . 

Characterization of polymers 5-9 was achieved by XH and 31P NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry, UV/visible and infrared spectroscopy, and elemental microanalysis. All the polymers were soluble in common organic media, such as tetrahydrofuran, acetone, and methylethyl ketone. 

A typical 31P NMR spectrum consisted of a sharp, singlet resonance at -8 ppm, presumably a consequence of the similar environment at the trifluoroethoxy and ethoxy-ether substituted phosphorus atoms in the mixed-substituent system. In addition, the singlet resonance indicated a high degree of chlorine replacement. This was supported by the elemental microanalysis data. 

Pell, E., L. Machherndl, and H. Malissa Recent Results in Relative Conductometric Elemental Microanalysis. Microchem. J. 10, 286 (1966). 

The solid was identified as 5,6-bis(4-methoxyphenyl)-3-methyl-l,2,4-triazine by nuclear magnetic resonance analysis, mass spectrographic analysis, and elemental microanalysis. 

Aryl azides may be characterized by the usual methods of chemical analysis. Their ultraviolet and visible absorption properties described earlier, are distinctive. The weak shoulders at 280 to 290 nm are characteristic and are usually visible if they are not obscured by their major absorption band. For example, phenyl azide itself has X,max 250 nm with shoulders at 277 and 286 nm. In the infrared, arylazides absorb strongly with a peak between 2,100 and 2,160 cm-1 which is often split due to Fermi resonance (Av = 50 cm-1). Elemental microanalysis (forC, H, N) gives the expected values for pure aryl azides. Many examples of UV, IR, and NMR spectra of aryl azides are given in the literature cited. 

The microscope used in obtaining the results presented in this paper was a Vacuum Generators HB-5 STEM. A Kevex energy dispersive x-ray spectrometer, EDS, with 10mm2 Be window was used for the elemental microanalysis. 

The essential elements of an electron microprobe are the electron column and the wavelength dispersive spectrometers (Fig. 8.5). The electron column is very similar to that of a scanning electron microscope. Certain elements are added to it (such as a beam controller, viewfinder, etc.) to make it an instrument dedicated to elemental microanalysis. 

Ingram, G. (1962). Methods of Organic Elemental Microanalysis. Reinhold, New York. 

Trimethyl- (TriML) and triethyllead (TriEL) compounds were obtained from Alfa products (Johnson Matthey) and their purity was verified as follows carbon, hydrogen and chloride relative masses in the TriML and TriEL calibrants were determined by elemental microanalysis the chloride concentration was determined by ion chromatography. Total lead was determined in the calibrants by electrothermal atomic absorption (ETAAS) using two different acid digestion procedures (concentrated nitric... 

Elemental Analysis. Elemental analysis was carried out by Elemental Microanalysis Limited (Devon, U.K.). Prior to shipping, the samples were dried for 24 h at 100 °C under nitrogen before the measurements were made, they were dried again for 3 h under the same conditions. 

G. Ingram,Afef/jods of Organic Elemental Microanalysis, Chapman and Hall, London, 1962. 

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